Patterns of diversity across space: Islands as a case study
Announcements
- I’ve had a grading backlog. Sorry!
- Activity submission for this week: will be posted on Moodle, but completion is optional.
(Complete this for your own learning; not for points). - This week, Friday will be dedicated to discussing your Semester Project.
As we often do, let’s simplify the complexity
What about biodiversity patterns at smaller spatial scales?
Start at the simplest level: an isolated area
- i.e. an island that recently formed
- what determines how many species live on it in the long term?
Processes that govern species richness:
↑ by immigration of new species
↓ by local extinction (‘extirpation’) of existing species
↑ by local speciation
Let’s assume speciation is very slow and not relevant to our dynamics
Processes that govern species richness:
- ↑ by immigration of new species
- ↓ by local extinction (‘extirpation’) of existing species
- What determines rate of immigration of new species and local extinction?
Rates of immigration
What determines rate of immigration?
- Proximity to source (“mainland”)
- When an island is closer to the source, more new species can end up there
- Number of species already on the island
- If all the species from the mainland are already present on the island, then nothing new can immigrate in
On the following graph, draw 2 lines: one for an island close to the mainland, and one for a distant island (assuming both islands are of the same size)
On the following graph, draw 2 lines: one for an island close to the mainland, and one for a distant island (assuming both islands are of the same size)
On the following graph, draw 2 lines: one for an island close to the mainland, and one for a distant island (assuming both islands are of the same size)
Rates of local extinction
What determines rate of local extinction?
- Size of island
- On smaller islands, species are more likely to go extinct just by randomness (“stochastic” extinction of smaller populations)
- Number of species already on the island
- If there are lots of species on the island, that means the number of possible extinctions is higher
On the following graph, draw 2 lines: one for a big island, one for a small island (assuming both islands are equally far away from the mainland)
On the following graph, draw 2 lines: one for a big island, one for a small island (assuming both islands are equally far away from the mainland)
On the following graph, draw 2 lines: one for a big island, one for a small island (assuming both islands are equally far away from the mainland)
Putting the two together
Actual islands are not the only “islands” out there
Lakes
Habitats with patchy distribution
Human–modified landscapes
“[The concept] might well have languished in the cabinet of academic curiosities had not conservation biologists realized a decade or so ago that human activities, by fragmenting natural habitats, were creating island from previously continuous populations.” - Brussard (1997)
Some insights extend relatively cleanly
Bigger ‘islands’ (like big national parks) are more likely to support a diversity of organisms than smaller ones
Conservation areas that are near large “sources” are likely to be more diverse than isolated conservation areas
But complications can arise when we want to generate insights for conservation
- If you know that you can set aside 500 square km for conservation, should you…
- Have one big conservation area (a big ‘island’)?
- Or, have 10 smaller conservation areas of 50 square km each?
- Or, have 100 tiny conservation areas?
- “SLOSS” (Single Large Or Several Small) debate - all the rage in the 1970s-80s in conservation
Team Single Large
- Bigger conservation areas ensure lower extinction rates, because each species can grow to larger population sizes (rather than a bunch of small populations, each of which might blip out)
Team Several Small
- One big conservation area might miss some habitat heterogeneity, and only select for a small group of species
- Even if a species goes locally extinct (‘extirpated’) from one site, it can immigrate in from another area
Team Single Large
- Some species, especially large mammals and many trees need large areas to survive – e.g. for a wolf pack to have enough food, there needs to be enough prey - so a small patch might be useless
and so on, and so on…
Eventually, conservation has become a very ‘local’ problem:
What is possible to conserve in any one locality?
What are the key species, and what is their population distribution?
How can we maximize total amount of land and hetereogenity of habitat?
What does a “large” conservation area even mean? How do roads change the landscape?
Almost as important as total area, is the connectivity between islands.
Patterns of diversity across space: Islands as a case study
https://www.nature.com/articles/s41586-020-2022-5
Real “islands” are not the only “island”-type systems
https://www.jstor.org/stable/pdf/2386606.pdf
- Just like the Latitudinal diversity gradient, patterns in species richness across islands are highly conserved.
What determines the biodiversity of an island?
- Size of the island
- Distance to a “mainland”
Expected relationship between immigration rate and species richness for a near and far island
Expected relationship between immigration rate and species richness for a near and far island
Expected relationship between immigration rate and species richness for a near and far island
Expected rate of species extinction on a big vs. small island
Expected rate of species extinction on a big vs. small island
Expected rate of species extinction on a big vs. small island
Putting the two together
This leads to the expectation that big islands, and islands close to the mainland, are more diverse than small islands, or those far from mainlands
- How does this relate to habitat conservation?
How does this relate to habitat conservation?
What management decisions can we make to maximize biodiversity?
Simple extensions: protect larger “islands” of natural habitats, e.g. state- and city-parks
And try to keep protected natural habitats closer to “mainland” sources, e.g. large national parks and conservation areas
Recent advances in Island Biogeography
- Size and distance are important, but so is connectivity between patches
- Increase in immigration rate
- Decrease in extinction rate.
Connectivity between islands is important to buffer from extinctions
But, the importance of connectivity can also arise through more “indirect” effects
Case study: Island biogeography of soil bacteria and fungi
In contrast with the considerable knowledge on the island biogeography of higher organisms, we know little about the distribution of microorganisms within and among islands
Study methods
A cluster of 29 islands with minimum levels of human disturbance was selected as our study sites (Fig. S1). The size of the 29 islands varies from 0.08 to 1153.87 ha.
On each island, we established one to six permanently marked 20×20 m2 plots, with the number of plots roughly proportional to island area on the logarithmic (log10) scale. What does this mean?
For each quadrat on the islands and mainland, four evenly distributed soil cores (3cm diameter to 10cm depth) were taken and mixed to form one composite sample, resulting in a total of 306 soil samples.
Study methods
Soil DNA was extracted by the MoBio PowerSoil DNA extraction kit (MO BIO Laboratories, Carlsbad, CA, USA).
Methods
- Alpha and Gamma diversity of each sample/island
Results
Bacterial gamma diversity
Results
Fungal gamma diversity
Results
Bacterial alpha diversity
Results
Fungal alpha diversity
Semester project checkin
Reminder of the project remit
Text from semester project overview
Reminder of the project remit
We are living in a weird time to be an ecologist. Thanks to technological advances, ecologists now have access to data and computational power on a scale that we couldn’t have imagined decades ago. At the same time, the consequences of global change are making themselves felt in all aspects of our life.
Given this context, ecologists needs to be persistent and creative in thinking about how the fundamental question that drive our field relates to the environmental challenges unfolding around the world.
Thus, the format for this course’s Semester Project is an “UnEssay” assignment.
The prompt for the unessay is to engage your curiosity by picking a natural system anywhere in the world, and explore+communicate its ecology and environmental challenges in any format you wish.
Many of you discussed a desire to engage in research experiences. This project is designed to help you think like a researcher.
Reminder of the project remit
Your unEssay should provide the audience an overview of how the four central themes in ecology introduced in the course play out in your focal system:
- Ecological systems are dynamic, meaning that their properties can change over time.
- Ecological systems feature feedacks, meaning that the dynamics of one component of a system often affects another.
- The dynamics and wellbeing of ecological systems are tightly intertwined with the dynamics and wellbeing of human societies.
- Understanding ecological systems requires us to confront uncertainty, which can arise because of limited knowledge of the system, or due to inherently stochastic processes.
Reminder of the project remit
In addition to general information about the system that you can gather from any number of reputable sources (textbooks, scholarly websites, etc.), I also expect that your unEssay be inspired by and reflect the details of at least three peer-reviewed academic articles.
Semester project so far
- List of potential ecological communities
- List of potential formats
- Annotated bibliography
What’s coming up
- “Formal project proposal”
- Final project submission
Formal project proposal
Due at the end of the week (Nov. 17th); details on Moodle. Can be completed as a written essay or video recording
Part 1: The ecological system
Introduce your ecological system with the relevant information for giving context to your project (where, abiotic properties, key biological players, etc). How do the four core themes of Ecology play out in your system?
Part 2: The message you want to convey
What do you want your audience to learn about your focal community? How do you want your project to affect your audience?
Part 3: Details of the project format
E.g. if you are doing a podcast, how long will it be? Or if you are making infographics, how many will you want to make, and of what size? etc.
Part 4: What will you learn
E.g. What have you learned already about your ecological community that has surprised you, and that you think will surprise your audience? What are some skills that you will have to develop to complete this project?
Part 5: How do you define success for this project?
At a personal level, why did you choose to focus on this ecological system and on this format? What do you hope to get out of completing this project?
Part 6: Sharing your work
What is the most effective way to get your classmates excited about your project? Would you like to share this Semester Project publicly on the Course Website?
Final submission
- Complete the project itself
- Also complete a reflective essay (or video essay) about your project
- This can be a “final” version of the Project Formal Proposal
- Participation in “Project Fair”
- You will be asked to evaluate your own project, following a rubric.
Patterns of diversity across space: Islands as a case study